Pharmaceutical agents used to treat osteoporosis significantly reduce fracture risk via different mechanisms that ultimately enhance either structural or material biomechanical properties. Bisphosphonates such as Alendronate (ALN) increase structural bone strength almost entirely by promoting increased bone volume and density, but at the expense of impaired material properties. Raloxifene (RAL) minimally affects bone mass yet significantly improves material properties leading to an enhancement in overall bone strength. The goal of this BIRT revision is to test the hypothesis that pharmacological treatment with RAL enhances skeletal hydration and these changes correlate with enhanced biomechanical properties. Skeletal hydration has known effects on bone mechanical properties and preliminary data generated in our laboratory show enhanced skeletal bound water with RAL-treatment. Using longitudinal in vivo ultrashort echo time (UTE) magnetic resonance imaging (MRI) scans we aim to determine how ALN, RAL, and their combination affect skeletal hydration (bound and free water). To achieve this goal we have established a new collaboration with experts in medical physics/imaging who have experience with UTE-MRI. Specifically, the experiments in this BIRT will test the hypotheses that 1) Monotherapy with RAL, or combination treatment with RAL and ALN, will increase the total hydration and the bound water fraction in bone as measured by UTE-MRI compared to other treatment groups and 2) Increased total hydration and bound water fraction as measured by UTE-MRI will increase the energy required to fracture the bone, and will be positively correlated to improvements in bone toughness. The data generated in this project will provide the first evidence of how pharmacological agents modulate skeletal hydration in vivo and how this relates to the biomechanical properties of the bone. As UTE-MRI can be utilized in humans, these data have the potential to launch a new focus area for non- invasive methods of fracture risk assessment.